1. Field of the Invention
The present invention relates to an apparatus for detecting pinching of an object of a power window and, more particularly, to a method of detecting the pinching of an object of a power window apparatus, which prevents erroneous detection of the pinching of an object caused when a normal pulse edge interval cannot be detected due to no supply of a two-phase pulse from a pulse generating unit coupled to a motor for opening and closing windows.
2. Description of the Related Art
Hitherto, in order to prevent an object from being pinched in a window and damaged at the time of window closing operation and prevent an excessive load from being applied to a motor used for opening and closing the windows, a power window apparatus for opening and closing the windows of a vehicle, which detects the pinching of an object and either stops the motor or opens the window when occurrence of the pinching of an object is detected is known.
A known power window apparatus which detects the pinching of an object comprises at least a motor for opening and closing windows, a motor driving unit for driving the motor, a pulse generator which is coupled to the motor and generates a pulse when the motor rotates, a microcomputer control unit (MCU) for controlling the whole operation of the apparatus, and an operation switch for opening and closing the windows by manual operation.
The operation of the known power window apparatus which detects the pinching of an object is carried out as follows. When any of switches in the operation switch is operated, a drive signal from the microcomputer control unit is supplied to the motor via the motor driving unit to rotate the motor forward or reverse in accordance with the operated switch and allow the window to be opened or closed. When the motor rotates, the pulse generator coupled to the motor operates and generates a pulse. The microcomputer control unit acquires a pulse edge interval of the pulse generated from the pulse generator by counting clock signals, obtains a motor torque value from the calculated pulse edge interval, and compares the acquired count value with a base value which is preliminarily set in an internal memory. When the motor torque value becomes considerably larger than the base value, occurrence of the pinching of an object in the window is determined and the motor is immediately stopped or rotated in reverse.
According to the known power window apparatus which detects the pinching of an object as mentioned above, in case of opening or closing a window, the motor torque value is obtained on the basis of the pulse edge interval of the two-phase pulse generated from the pulse generator and compared with the base value, thereby determining the presence or absence of the pinching of an object in the window.
According to the known power window apparatus which detects the pinching of an object, in case of opening or closing a window, while a pulse is generated from the pulse generator, the presence or absence of the pinching of an object in the window can be determined on the basis of the pulse edge interval of the pulse. When a failure in a magnetic sensor provided in the pulse generator, a break in a cable through which a pulse generated from the magnetic sensor is led to a microcomputer control unit, a break or contact failure of a cable connector disposed on the pulse generator or microcomputer control unit side, or the like is caused by a some reason during the window opening or closing operation, the pulse is not generated from the pulse generator or not transferred to the microcomputer control unit. When the pulse generated from the pulse generator is not transferred to the microcomputer control unit, the microcomputer control unit cannot obtain either the pulse edge interval or the motor torque value based on the pulse edge interval. Consequently, there is a problem such that even if an object is pinched in the window during the period, the pinching of an object cannot be detected. On the other hand, when the pulse generated from the pulse generator is a two-phase pulse and only one phase in the two-phase pulse is not transferred to the microcomputer control unit, even if the microcomputer control unit can obtain a pulse edge interval, the pulse edge interval becomes about twice as long as the inherent pulse edge interval and the motor torque vehicle based on the pulse edge interval accordingly doubles. Consequently, a problem such that even when an object is not pinched in the window, occurrence of the pinching of an object is erroneously detected.